Electrolytic capacitors (e.g., tantalum capacitors) are increasingly being used in the design of circuits due to their volumetric efficiency, reliability, and process compatibility. For example, one type of capacitor that has been developed is a solid electrolytic capacitor that includes an anode (e.g., tantalum), a dielectric oxide film (e.g., tantalum pentoxide, Ta2O5) formed on the anode, a solid electrolyte layer, and a cathode. The solid electrolyte layer may be formed from a conductive polymer, such as described in U.S. Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 to Sakata, et al., U.S. Pat. No. 5,729,428 to Sakata, et al., and U.S. Pat. No. 5,812,367 to Kudoh, et al. The conductive polymer electrolyte of these capacitors has typically been formed through sequential dipping into separate solutions containing the ingredients of the polymer layer. For example, the monomer used to form the conductive polymer is often applied in one solution, while the catalyst and dopant is applied in a separate solution or solutions. Such sequential application of the solutions, however, is time consuming and not generally cost effective. Attempts have been made to use a polymerization solution containing both the monomer and the catalyst. However, such a single solution is not always practical due to the difficulty in achieving an acceptable life span for the solution. That is, when mixed together in solution with the oxidative polymerization catalyst, the monomer tends to prematurely initiate polymerization while still in solution and prior to application to the anode part. This premature polymerization may lead to an increased number processing steps and ultimately degrade the conductive polymer layer.
As such, a need currently exists for an improved method for forming a conductive polymer layer on an electrolytic capacitor from a polymerization solution.